The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Gastropod Grazings

Generally considered a garden and farmland pest, the garden slug can also produce abstract art, as a result of grazing on the algae of flat surfaces. These intriguing patterns, as photographed on the siding of a house, are the handiwork of the Limax Maximus, one of many species of gastropods (translates as stomach-foot). Native to Europe and the Mediterranean countries of Africa, this herbivorous, great grey slug, also referred to as the leopard slug due to the spots on its body, is present in 46 of the 50 U.S. states. It's common in warm, humid environments, and can grow up to 4 in (10 cm) long.

These zigzag tracks are evidence of one of the slug’s eating behaviors made by its radula (comparable to a tongue) that contains chitinous ribbons or rows of hundreds of teeth (also known as denticles.) The radular teeth, continually being worn down and replaced, are used as a rake to scrap diatoms and algae with the slug’s downward facing mouth before the food is eased into the esophagus with the help of sticky mucous. The slug’s actual feeding activity is rarely observed first-hand, as slugs are typically more industrious at night, in rainy weather or in damp greenhouses or crawl spaces.

The width of the zigzags range from about 1/4 in (0.6 cm) to 1/2 in (1.3 cm).The bottom photo shows a size comparison of the patterns with the photographer’s thumb. Photos taken March 16, 2016.